Electrical heater for thermal relays



July 25, 1933.- c H CHAPMAN 1,919,975

ELECTRICAL HEATER FOR THERMAL RELAYS Filed March 18 1930' I I I fi Inventor Charles H. Chapman, b5 W I'Iis Attoheg.

Patented July 25, 1933 UNITED STATES PATENT {OFFICE CHARLES H. CHAPMAN, OF SCOTIA, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK ELECTRICAL HEATER FOR THERMAL RELAY S Application filed March 18, 1930. Serial No. 436,816.

My invention relates to electrical heaters for thermal relays, and more particularly to a removably mounted electrical heater of small current capacity for thermal relays of the bimetallic type.

As set forth in the copending application Serial No. 486,870, filed March 18, 1930, by Lewis J. Weber, andassigned to the assignee of the present invention, electrical heaters of different current carrying capacity are required when the bimetallic thermal relays are employed forfproviding time ,element overload protection or electric motors of different ratings. To facilitate interchange of the heaters, they must be readily .removable. To obtain the maximum heating eificiency, the heater must be arranged to substantially surround the bimetallic element. For the larger current carrying capacities, these requirements may be readily met since the resistance wire or other material of which the heaters are formedis of suflicient size to be formed into a self-sustaining coil surrounding the bimetallic element. However, for the smaller current carrying capacity, the resistance wire necessarily is of such small size as to" require some form of sustaining support in order to maintain the resistance wire in proper operating position with respect to the thermal element. v The principal object of the present invention is to provide an improved form of small current capacity electrical heater for the thermal relays which may be mounted for ready removability and-which insures that the resistor wire is maintained in the proper positionsurrounding the thermal element.

In the accompanying drawing Fig. 1 is a 4 perspective view showmg a bimetallic type ,of thermal relay provided with the improved form of removably mounted small current capacity electrical heater with the parts of the relay in disassembled relation, 4 and Fig. 2 is a sectional view of the thermal relay with the electric heater in operative position surrounding the thermalelement.

In Fig. l the thermal relay is shown as used in connection with the electromagnetisally operated switch 10 which is mounted on the base 11 from which the terminal su ports 12 and 13 extend for mounting tie thermal relay thereon. The thermal relay comprises the substantially L-shaped channel frame 14 upon which the bimetallic thermal element 15 is fixed at one end with the other end 15 in abutting engagement With the movable member 16 which is rotatably mounted by the pin 17 on the frame 14. The spring 18 serves to bias the movable mcmber 16 into abutting engagement with the free end .15 of the thermal element. When the thermal element 15 flexes to release the movable member 16, the latter engages with the bar 19, which is pivotally mounted upon the pin 20 and is argagement with the contact 22.

The small current capacity electric heater 25 is provided for heating the thermal element 15 to cause fiexure thereof. In accordance with the present invention the elec trical heater 25 is formed .of the two channel shaped terminals 26 and 27 between which extend the notched su porting strips 28 and 29 of suitable insu a'ting material such as mica or the like which are offset with respect to the fiat portions ofvtheterminals 26 and 27 which enga e the terminal supports 12 and 13. The si es 30 and 30, of the channel shaped terminals 26 and 27 are bent over the ends of the strips 28 and 29 so as to firmly secure the strips in opposing spaced relation. The resistance wire 31 is of relatively small size so as to become heated with a current of relatively small value passing therethrough.

In order to removably support the resistance wire 31 in proper operating relation SHII'O11I1d1I1% the thermal element 15, as shown in. ig. 2, it is wound around the notched supports 28 and 29. The ends of the resistance wire 31 are secured to the termmals 26 and 27 by the bent over clips 32 and 33, preferably being soldered or brazed thereto.

With the small capacity heater constructed in the manner just described, the movable member 16 may be swung out of engagement with the end 15' of the thermal element and ranged to actuate the contact 21 out of enthe heater slipped over the end thereof so as substantially to surround the thermal element with the turns ofelectric heater 31, as shown in Fig. 2. The terminal 26 of the heater element together with the upstanding lug 34 of the frame 14 is then secured to the support 12 by means of the holding screw 35. The lower terminal 27 of the heater is secured in a similar manner to the support 13 by the screw 36. To place the relay in operative condition, it is now only necessary 'to release the tripping member 16 to permit the same to turn'about the pin 17 in accordance with its bias so as to engage with the free end 15' of the thermal element 15, as

shown in Fig. 1.

With the supports 12 and 13 connected in an electric circuit, the current flowing therebetween through the resistance element 31 generates heat which is transmitted to both sides of the thermal element 15. The notched supports of insulating material serve to maintain the turns of the resistance wire out of actual engagement with the thermal element while providing sufiicient space 'between the turns for free movement of the thermal element out of abutting engagement with the biased member 16. In this way an eflicient and reliable electrical heater of small current carrying capacity is provided for the thermal relay.

What I claim as new and desire to secure by Letters Patent of the United States is 1. A removable electric heater for a ther mal element comprising-a pair of laterally spaced, notched insulating supporting strips, a resistor wire wound in the notches of said I strips to form a heater coil for surrounding the thermal element, and metallic terminals fonthe respective ends of said coil, each terminal bein provided with dependin legs for supportingsaidinsulating strips an with a contact portion located at one side of said legs so as to permit the insertion of the thermal element through the open ends of said coil and between said strips.

2. A removable electrical heater for a bi- 3. A removable electric heater for a thermal element comprising a'pair of laterally spaced, notched insulating supporting strips, a resistor wire wound in the notches of said strips to form a heater coil, said strips being so dimensioned as to support said coil in spaced relation with the thermal element,

and metallic terminals for the respectiveends of said coil, each terminal being provided with depending legs clamped around the ends of said stripsfor holding said strips in said laterally spaced relation, and with a contact portionlocated at one side of said legs so as to permit the insertion of the thermal element, throughthe open ends of said coil and between saidstrips.

' CHARLES H. CHAPMAN. 

